Referring to FIGS. 1 and 2, U.S. Pat. No. 8,544,522B2 discloses a conventional window blind 1 that includes a headrail 11, a blind body 12 and two spaced-apart control units 13. The blind body 12 is hung from the headrail 11 and is expandable and retractable relative to the headrail 11 in an up-down direction. The blind body 12 has a fixing portion 121 connected to the headrail 11, a bottom portion 122 spaced apart from the fixing portion 121, and a plurality of parallel folding portions 123 arranged in the up-down direction between the fixing portion 121 and the bottom portion 122. Each of the control units 13 has a control cord 131 operable to retract and expand the blind body 12, a plurality of rings 132 respectively connected to the folding portions 123 of the blind body 12, and a spacer cord 133. For each of the control units 13, the spacer cord 133 has a main cord portion 134, a plurality of first cord portions 135 spaced apart in the up-down direction and connected to the main cord portion 134, and a plurality of second cord portions 136 connected to the main cord portion 134 and arranged in a manner that, between each adjacent two of the first cord portions 135, there is at least one of the second cord portions 136. Each of the second cord portions 136 is twisted to form a substantially figure-eight shape containing two cord loops 137. The main cord portion 134 has an upper end connected to the headrail 11, and a lower end connected to a lowermost one of the rings 132.
Specifically, the control cord 131 passes through the headrail 11, and has a front section (not shown) disposed in front of the blind body 12 for being operated by a user, and a rear section (as illustrated in FIGS. 1 and 2) disposed behind the blind body 12, downwardly passing through the rings 132, the first cord portions 135 and the cord loops 137 of the second cord portions 136, and finally fastened on the lowermost one of the rings 132.
By virtue of the configuration of the cord loops 137, when the control cord 131 is pulled in a horizontal direction, each of the second cord portions 136 and a corresponding part of the control cord 131 are tightly entwined together to form a knot (similar to an over hand knot), thereby preventing the control cord 131 from being overpulled which may dangerously entangle a child who plays with it.
However, when assembling the abovementioned conventional window blind 1, an operator needs to twist each of the second cord portions 136 to generate the loops 137 for extension of the control cord 131. Since the conventional window blind 1 has a substantial number of the second cord portions 136, and since each second cord portion 136 is relatively short, the abovementioned assembling process is difficult and time-consuming.